Comparison between the effects of TiO2 synthesized by photoassisted and conventional sol-gel methods on the photochromism of WO3 colloids

WO3 colloids can exhibit a blue color under UV-light irradiation due to the absorption of electrons trapped at the energy levels within the forbidden gap and this coloration performance can be improved by TiO2 nanoparticles. In this work, it is found that TiO2 prepared by the photoassisted method (TiO2-P) exhibits stronger enhancement effects than that prepared by the conventional sol-gel method (TiO2-C). Several possible mechanisms have been proposed to account for this phenomenon. The migration of charge carriers toward different directions is promoted since the flat-band potential of TiO2-P colloids is more negative than that of TiO2-C and the contact between WO3 and TiO2 particles is improved in the WO3/TiO2-P system; there are more efficient TiO2 and hole scavengers (i.e., Ti3+ and/or TiO2-O2*- species) in the system containing TiO2-P; the bandgap of TiO2-P becomes narrowed, and so on. In addition, the potential applications of this process are also discussed briefly.